This invention relates generally to internal combustion engines, and more particularly to an improved compression release mechanism for four-stroke cycle engines.
Compression release mechanisms for four-stroke cycle engines are well known in the art Generally, means are provided to hold one of the valves in the combustion chamber of the cylinder head slightly open during the compression stroke while cranking the engine. This action partially relieves the force of compression in the cylinder during starting, so that starting torque requirements of the engine are greatly reduced. When the engine starts and reaches running speeds, the compression release mechanism is rendered inoperable so that the engine may achieve full performance. It is normally advantageous for the compression release mechanism to be associated with the exhaust valve so that the normal flow of the fuel/air mixture into the chamber through the intake valve, and the elimination of spent gases through the exhaust valve is not interrupted, and the normal direction of flow through the chamber is not reversed.
Examples of compression release mechanisms for four-stroke engines are shown in U.S. Pat. Nos. 3,381,676; 3,496,922; and 3,897,768; all assigned to the assignee of the present application. Although prior art compression release mechanisms are generally effective for relieving compression in the cylinder during cranking the engine, these prior art mechanisms are typically designed to provide compression relief when the exhaust valve is located inboard on the camshaft relative to the cam gear. U.S. Pat. Nos. 3,496,922 and 3,381,676 are examples of such compression release mechanisms. U.S. Pat. No. 3,897,768 discloses a compression release mechanism that is operable to actuate the exhaust valve when said valve is located outboard of the cam gear. Although this prior art mechanism performs satisfactorily, it has more working parts than is desired, and also imparts more friction to the system than is desired.
Accordingly, it is desired to provide a compression release mechanism that is effective in operation and relatively simple in construction, and that may be utilized to actuate the exhaust valve in an internal combustion engine wherein the exhaust valve is located outboard of the cam gear.